Here's my recent metaball-demo, called Lava. I got tired of the
usual 'pile of metaballs blobbing around'-scene and made a worm out of
connected metaballs chasing some particles. Looks crappy in still
screenshots, try the demo for a better effect :)

The metaballs are rendered environment mapped with the 'marching pyramids'-
algorithm, and they are connected to each others with the particle/spring
system from the 'Advanced Character Physics'-article. The metaball surface
is rendered in slices one cube high, and the surface is tracked similarly
as in an article at AngelCode. The worm is made out of 10 metaballs,
connected by 9 springs. It's written in C++ / DirectX 8.1

Additionally there are 10 balls of light flying around, trying to stay
close to the worm. Two of the worms have a lightsource attached to them,
lighting the scene.
Runs at around 60-90 fps on my AMD XP2000+ / GeForce2 GTS, probably needs
a T&L-card to run.